DE2363245A1 - DRIVE SYSTEM - Google Patents

Description

DIFL-ING.

HELMUT GÖRTZ

6 Firarikiurt aon Main 70
khnecfcanfrofctr, 27-TaI. & i 7Ö79

December 17, 1973 Gze / Ro

Motorola, Inc. Franklin Park, Illinois / USA

Drive system

The invention relates to a drive system; In particular, the invention relates to a drive system for cassette tape recorders especially for very flat cassette tape recorders.

Cassette tape recorders usually require three to four inches of housing to accommodate the cassette To create drive system and other components of the tape recorder. In the case of tape recorders for automobiles, the height represents Such housing is a problem ", since the tape recorders usually placed under the dashboard and thus protrude into the area where the legs are located of the passengers. It is also desirable to miniaturize cassette tape recorders as well as others electronic equipments have been miniaturized in recent years. Portable record player, radio and television receivers, for example, have already been largely downsized to facilitate their portability.

One problem with reducing the height of a tape recorder is the need to use a large flywheel to have to achieve a constant belt speed.

409830 / Ö725

QRKaiNAL INSPECTED

Flywheels of tape drive systems usually have a diameter of 10 to 12.5 cm and a thickness of 0.65 to ₁₉ 3 cm. The flywheel acts as an energy storage unit and is required to maintain an essentially constant belt speed and thus good sound quality in the event of torque fluctuations in the drive motor. Such fluctuations in the torque can be based on tape displacements, a short-term sticking due to the tape sticking to the capstan, a tape split or, for example, on an adhesive pressure roller bearing.

In view of the need for this energy storage and for generating a sufficiently high torque for rapid acceleration to operating speed, a reduction in the size of drive systems, including the drive motor and the flywheel, poses problems. Available motors had axial dimensions ₉ which did not allow their use in a very flat housing. In addition, complex circuits were required to initially supply sufficient current to accelerate the drive to operating speed and then to limit the current to the operating value without generating vibrations in the motor power supply that would affect the operation of the belt drive.

In a known device, the problem of reduction the engine dimensions, concerns to ~ there is a slip ring armature a stator formed by a permanent magnet

■ z _

409830/072

- 3 -

is det, or consists of magnetizable material. Even though With this arrangement, a certain reduction in the motor dimensions is possible with the same power output Nevertheless, a flywheel is still needed to achieve the necessary drive stability.

Effective speed control devices present a further difficulty represents the stability and a constant engine speed under different temperature conditions to ensure. Such a known motor control device for maintaining a substantially constant speed A tachometer arrangement with a disk-shaped permanent is used over a certain temperature range -Magnets as a rotor that rotates coaxially in the field of the motor. However, this known, very special device is not suitable for use in a tape recorder of the desired size and dimensions.

The object of the invention is therefore to provide a compact drive system for a flat cassette tape recorder, that is to say a tape recorder with small vertical dimensions.

Another object of the invention relates to a small DC motor with a rotor, which has an annular permanent magnetic structure, which has a wound stator surrounds.

Yet another object of the present invention is an improved DC motor having an annular permanent magnet for the rotor structure, 'which is to be operated at relatively high speeds in order to achieve a steady torque deliver. 409830/0725

Furthermore, an improved speed sensor is to be created, which is controlled by the motor of a cassette tape recorder coupled to the speed of the drive.

Further objects and features of the present invention result from the description, the drawings and the claims.

The drive system according to the invention for a cassette tape recorder for an automobile or similar vehicle comprises a DC motor which has a stator with three windings in a star connection and with commutation for successive excitation of the windings. The rotor includes a ring made of permanently magnetized material that coaxially surrounds the stator. A drive wheel is attached to the rotor shaft and firmly coupled by means of a drive belt to a reduction pulley, which is connected to the capstan of the tape drive is. The drive belt is also guided around a guide roller and extends to produce a good one frictional connection over more than half of the circumference both the drive wheel and the reduction pulley.

A speedometer generator has a ring gear made of magnetic material, which is attached to the rotor, with alternating Teeth and gaps adjacent to a ring magnet that has twice the number of magnetic segments,

- 5 40 98 30/0725

as the number of teeth in the ring gear. In the vicinity of the ring magnet there is a coaxial test or probe coil in which a current is induced, the frequency of which is a function of the rotor speed. The coil is with a control circuit for controlling the engine speed according to the frequency changes in the test or Special coil connected to induced current. The control circuit comprises an operational amplifier with a negative one Feedback loop, which includes a double-T filter, which allows a narrow frequency band to emerge. The op amp provides a low output when the engine is running starts and the speed of rotation of the motor increases to the desired number of revolutions in order to pass the current through to enable a transistor which supplies the motor with power from the direct current source. When the start switch is closed, maximum current flows to the motor until the speed of rotation of the motor reaches the desired number of revolutions at which the negative feedback is reduced to the output signal of the amplifier and cut off the power supply to the motor.

The present invention thus relates to a drive system for very flat cassette tape recorders with a direct current motor, which has a stator with several field windings and a rotor with a permanent ring magnet that supports the stator surrounds coaxially. Brushes on the rotor touch contacts. On the stator, to energize the field windings sequentially. One with

- 6 - ■ 409830/0725

The drive wheel connected to the rotor is via a drive belt, with a capstan pulley that is larger than the drive wheel is coupled to the capstan of the tape drive system to drive ρ where the faster rotating rotor one Exerts flywheel effect, and thus stabilizes the drive. A speedometer generator has a ring gear, which is connected to the rotor and a larger number on its circumference Has teeth that work together with segments of a coaxial ring magnet »A test coil adjacent to the ring magnet is connected to a control circuit which is coupled to the field windings of the motor to energize them, wherein the control circuit acts on the current supplied to the drive to allow additional changes in the motor speed. to compensate.

The drawings serve to explain the invention "without it to restrict.

Show it

1 shows a perspective view of a cassette tape recorder with the drive system according to the invention, "

2 in plan view, partially in section, the tape recorder · ■■ drive system according to the present invention?

3 shows the motor and the speedometer generator, partially in section, and a schematic diagram of the control circuit for motor j and.

40983 0/0725 - 7 -

4 shows the engine in a plan view, partially in section

of the tape drive system.

The cassette tape recorder according to FIG. 1 has a housing 10 with an opening 12 for receiving the tape cassette 14. The housing 10 has a height of approximately 28.6 mm (the vertical dimension is denoted by 16 in FIG. 1), a width of 165.1 mm (labeled 18) and a depth of 107.9 mm (labeled 20). The buttons 17 and 19 are used for control the sound, the volume and to switch it on and off.

The drive system for the tape recorder is shown in Figure 2 and includes a capstan 24 which is rotatable with respect to the base 26 of the housing 10 is arranged. When the tape cassette 14 is inserted into the opening 12, it touches therein contained tape 28 the capstan 24 and the tape head 30, with the pinch roller 32 within the cassette, which the tape keeps in driving contact with the capstan 24.

A square belt 34 made of flexible material, such as reinforced Rubber, connects the drive wheel 36 of the motor 44 to the reduction pulley 22. The capstan 24 is concentrically attached to the pulley 22 on this and is driven by this. A guide roller 38 that over the holding arm 40 is connected to the base plate 26 can be brought into various positions in order to achieve a suitable tension in the belt 34 to produce. The strap 34 extends extends over more than 180 ° of the circumference of the motor drive wheel and continues to extend by more than 270 ° of the circumference of the

- 8 409830/0725

Capstan reduction pulley 22, for the manufacture of a good frictional connection between the motor and the capstan.

The motor 44 (Figures 3 and 4) is operated with direct current and comprises a stator 46 with three windings 60, 62 and 64 thereon and a rotor 48 with an annular permanent magnet 50 which coaxially surrounds the stator. The rotor 48 includes a rotor or upper section 42 which is integrally fastened with the drive wheel 46 to the motor shaft 35, which in turn is rotatably arranged in the bearing 49 of the stator 46. The annular magnet 50 is held by an annular edge 43 which protrudes beyond the rotor 42. A pair of brushes 1 and 2, electrically connected to each other, are held by plate 57 of the rotor to come into contact with slip ring 66 and ring sections 68, 70 and 72 on the stator.

The stator 46 includes a laminated magnetic structure 58 (FIG. 4), which can be made of silicon steel, and three legs 58a, 58b and 58c with the three windings 60, 62 and 64 which are wound around the respective legs. Every of the windings! has one connected to the common point 59 Output (Figure 3) and a second output, which is connected to one of the slip ring sections 68, 70 and 72, which are arranged in a circle, axially offset, within the endless slip ring 66 (FIG. 4). The slip ring sections, 68, 70 and 72 are in turn with the slip ring

40983 0/0725

connected by the interconnected brushes 55 and 56, when the rotor 48 rotates. Hence the windings 60, 62 and 64 are alternately connected to point 59 and slip ring 66. The slip ring 66 is over the conductor and switch 78 connected to battery 80 while the common point 59 of the three windings with the rotation control circuit 82 is connected. As a result, the Closing the switch 78 alternately energizes the field windings from the battery 80 through the slip rings and brushes the rotor 48 moves.

The magnet 50 can be made of permanently magnetizable !! magnetic Material be formed, for example from rubber, which is impregnated with magnetic ceramic or ferritic material, or made of a different material with high coercive force «To the magnet 50 include two opposite active sections 51 and 52, each of which has a circular arc section of approximately 130 ° constitutes, which are separated from one another by inactive sections 53 and 54, the arc sections of about 50 ° turn off. The sections 51 and 52 are magnetized radially, so that one section (51) acts as the south pole on the rotor, while the other section (52) acts as a north pole on the rotor, so that a magnetic field is generated in which the windings 60, 62 and 64 work. The magnetic field is completed by the annular edge 43, which made of magnetic material. It is evident that the magnetic sections 51 and 52 are made up of flat magnets can be replaced with shaped pole pieces.

•. - 10 -

409830/07 2 5

No flywheel is used in the present tape drive. The reduction pulley 22 is attached to a place normally occupied by the flywheel, but it is much thinner than a conventional flywheel so that little energy is retained from it. The reduction pulley 22 therefore only provides a slight flywheel effect. The motor 44 with the direct (no slip clutch) coupling from the drive wheel 36 to the capstan pulley 22 provides a "flywheel effect" for the capstan of the tape recorder, whereby the eliminates need for a separate flywheel _t as will be explained.

The moment, ie the product of the effective mass times the distance from the axis of rotation, and the speed of rotation determine the amount of energy that is stored in the rotating structure of the motor. Since the rotor 48 carries the greatest part of its weight in de.r edge 43 and the magnet 50 around the circumference thereof guides the _s a to a distance to be considered for the moment which is approximately equal to the radius "and the torque is therefore considerably greater than Such a moment, which is generated by a uniform disc of the same weight »Second, the speed of rotation of the rotor 48 is considerably greater than that of the capstan 24 to which the flywheel is connected in conventional tape systems ρ so that the moment in question is further increased» The rotor 48 therefore also takes on the task of a flywheel. The relatively small reduction pulley 22 is light in weight, about a thickness of I ₉ 6 mm and a diameter of approximately 63 ^ 5 mm and can be made from

- 11 -

made of cast metal. With the smaller engine and no flywheel, less torque is required to do the same Flywheel effect to maintain a constant belt speed. Since there is no flywheel and less torque is required to start, starts the engine faster.

The speedometer generator or the speed sensing device * has a toothed ring or gear wheel 88 (FIGS. 2 and 3) which is connected to the rotor 48 of the motor 44 and itself. rotates within the ring magnet 90 held by the housing 91. A test coil 100 is also accommodated in the housing 91 and in this coil current is induced by the altered flux which is generated by the rotation of the wheel 88. The frequency of the induced current depends on the speed of rotation of the rotor 48. The speed of rotation control Circuit 82 is connected to test coil 100 via line 102 to determine the rotational speed to control the motor as a function of the frequency of the current induced in the test coil. A second line connects coil 100 to ground. As explained, the revolution speed control circuit 82 continues with FIG common point 59 of the motor field windings connected.

The gear or ring gear 88 of the speedometer, which is connected to the rotor 48, is made of soft mag-. material and includes a plurality of teeth 92 with spaces in between, e.g., with thirty-nine teeth. All teeth are the same size as one another

409830 / 072S - 12 -

just as the gaps are the same size, but teeth and gaps are not the same Must have dimensions. The ring magnet 90, which is adjacent to the teeth of the ring gear 88, is doubled Number of magnetic segments (78) divided, as the ring gear has 88 teeth, so that each segment is half Corresponds to the circumference of the arch of a tooth or space. Each annular segment has poles of opposite polarity on its opposite radial sides, with adjacent segments magnetized in opposite directions. The magnetic one Field extends from the magnet segment through the housing envelope 91 and through a ring 93 made of magnetic material, via an air gap to the edge 43 of the rotor 48 and from the edge to the gear 88 and via the air gap back to the Magnets. If the teeth 92 are adjacent - to the north poles of magnet 90, then the flux surrounds coil 104 in one direction and when teeth 92 are toward the south poles move in magnet 90 then the flux reverses. This leads to an alternating current in the coil 100.

Since the ring gear has a large number of teeth and a large number of magnetic poles are present, occurs over all the teeth and all poles averaging on. This opens up the possibility of an accumulated tolerance modulation of the signal in the coil 104, which results from the eccentricities of the construction, such as the toothed ring 88 or the segments of the ring magnet 90, decreased. The signal induced in the coil 100 is dependent on proportional (incremental) changes in the

- 13 409830/0725

speed of rotation of the motor, by means of which the teeth are moved past the magnetic poles at different speeds. For example, if tooth 93 is near magnetic segment 9h (FIG. 2), tooth 96 is near segment 98 at the same time. Rotation of gear 88 moves the teeth from the magnetic segments of one polarity to Segments of opposite polarity, whereby the magnetic flux emerging from the magnet segments, which penetrates the teeth, reverses the magnetic field in the coaxial test coil 100 and induces an alternating current signal therein, which changes in frequency with the proportional changes in the speed of rotation. The AC signal from the take-up coil 100 is applied to the control circuit 82 via line 102, as set out above. . '

It is evident that the speedometer will work even if the magnet 90 does not completely surround the gear 88, however, the output signal from the coil 100 is smaller, if not a magnet segment adjacent to each tooth 92 of the ring gear is provided.

The circuit diagram for the control system 82 of the drive motor is shown in FIG. That formed in the coil 100 The signal is amplified via the diodes 105 and 106, which are connected in opposite directions and which increase the amplitude of the alternating current signal prune or limit. The limited signal is transmitted via the

- 14 -409830/0725

Resistors fO8 and 109 reinforced, which are a voltage divider form to produce the desired signal level. Resistors 108 and 109 can also be replaced by a potentiometer. The output signal from the voltage divider is passed through the blocking capacitor 110 is applied to the base electrode of transistor 114. Resistors 112 and 113 provide a bias potential for the "base of the transistor 114. The transistor 114 amplifies the Viechselstromsignal> wherein the amplified signal is passed through the collector resistor 115. The resistor 123 and the capacitor 124, which between the emitter electrode of the transistor 114 and the ground are connected, increase the stability of the amplifier stage.

To select certain frequencies in the amplifier 114, a feedback circuit is provided with a double T-filter network 116, which transmits the signal from the collecting electrode of the transistor 114 to the base electrode of the transistor 118. The transistor 118 is linked to an emitter follower circuit , the output signal being passed on via the emitter resistor 120 and given back to the base electrode 114 via the blocking capacitor and resistor 122. The double-T feedback network 116 can be of a known type and it is designed so that it filters out a narrow frequency band ₉ to which the frequency of the signal generated in the coil 100 of the tachometer belongs when the motor is operated at the desired speed of rotation the network is designed so that there is one frequency

4 09830/0725 -15-

of 1.365 kHz filtered out.

When the motor is supplied with energy and its speed of rotation increases increases to the desired speed of rotation, then the frequency of the signal is from the tachometer coil 100 at the frequency which is filtered out by the filter network, so that a signal to the base of transistor 114 which is opposite to the signal from coil 104. Hence will the output signal at the collector of transistor 114 one have low value. The bias applied to the base of transistor 114 can be selected to provide the desired value Deliver value. When the motor has reached the desired speed of rotation, so that the frequency from the signal of the speedometer coil falls into the range of the frequency filtered out by the filter network value, then becomes essentially no signal is given to transistor 118 and its output signal is largely reduced, so that the negative feedback applied to the base of transistor 114 is likewise reduced. This will transistor 114 has an increased output on its Deliver the collector electrode.

To the collector electrode of transistor 114 is a circuit comprising a capacitor 125, a diode 126 and a Capacitor 128 connected. A voltage divider chain with the resistors 130 and 131 and the diodes 132 and 133 forms the connection between the resistors 130 and 131 is linked

- 16 409830/0725

through diode 134 to the connection between the resistors 125 and diode 126. This circuit forms and provides an integrator and voltage doubler detector DC control voltage across capacitor 128 as a function from the AC signal at the collector electrode of transistor 114. The one formed across diodes 132 and 133 Bias varies with temperature and provides temperature compensation for diode 126 and transistor 136 associated with it. The transistor 136 serves as an emitter follower circuit and provides a high external resistance for the · detector. That formed via the emitter resistor 138 Control signal is given to the base of transistor 140, which forms the driver stage for the output stage 142, which controls the current through the common conductor 59 of the field windings.

If by actuating the 'switch 78, the drive circuit is turned on, the transistor 142 is fully conductive to apply current to the winding, the current through the commutating action of the brush 56 and the ring sections 68, 70 and 72 is fed alternately to the three windings. Before the motor reaches the desired speed of rotation has reached, as explained above, the output signal of transistor 114 is so low that the found Voltage applied to the base of transistor 136 is also low. The transistor 136 is therefore be non-conductive and the driver transistor 140 will also be non-conductive, so that the output of the transistor 142 will guide completely. When the speed of rotation

- 17 409 8 3 0/0725

If the speed of the motor increases to the desired frequency, then the filter network 116 reduces the negative feedback to the transistor 114 so that its output becomes large. It leads to a sufficiently noticeable tension, which is applied to the base of the transistor 136 in order to make it conductive, whereby in turn the driver transistor 14O becomes conductive. When driver transistor 140 conducts, will its collector electrode is connected to the ground potential in order to switch off the output of the transistor 142. this will reduce the current through the common end terminal 49, which in turn reduces the excitation of the field windings of the motor. ■

The drive system described has been found to be extremely effective Proven to drive the sound waves in cassette tape recorders, which move the tape. By using a motor with a rotor that has significant momentum, a separate flywheel is not required. The construction of the Motor with a wound stator and a permanent magnet rotor, v / which surrounds the stator leads to a motor with very small axial dimensions, which nevertheless has the required Torque supplies. Since no flywheel is required, the pulley, which is connected to the capstan, can to drive them at reduced speed, be very thin. This allows such a drive system in one Turn to cassette tape recorder, which is not essential is thicker than the tape cassette itself. The tachometer structure with the motor supplies a signal, that of proportional (incremental) changes in the speed of rotation depends, which in turn is used to control the motor, so that

- 18- -. 409830/0725

whose speed of rotation can be kept very constant can. Since no flywheel is required apart from the "Flywheel effect" of the engine itself, the control of the revolution speed can be easily performed.

- 19 -

409830/0725

Claims (12)

Claims /i.)Antriebssystem .für ein'drehbaren drive shaft, marked ^ - ' characterized by a motor (44) with a stator (46) and a rotatably mounted rotor (48), with a rotor section which surrounds the stator coaxially, and Rotational speed reduction devices (22, 34, 36, 38) which constitute a coupling between the rotor (48) and the drive shaft (24), and the rotor (48) is of such a nature that a moment for energizing is generated around the rotational speed to keep the drive shaft largely constant. 2. Drive system according to claim 1, characterized in that a direct current motor is provided as the motor (44), with a wound stator (46) and a permanently magnetized ring-shaped magnet (50) belonging to the rotor (48), which surrounds the stator. 3. Drive system according to claims 1 or 2, characterized characterized in that to the rotational speed reduction devices a drive wheel (36) connected to the rotor and a reduction pulley (-22), which is connected to the drive shaft, a drive belt (34), which the clutch of the drive wheel to the reduction pulley (22), and a guide roller (38) is provided which the drive belt (34) in such a position that the lateral thrust from the drive wheel (36) is reduced . 403830/0725 - 20 - 4. Drive before devices according to claims 1, 2 or 3, characterized in that a wheel of magnetic material (88) is provided with teeth thereon, which is connected to the rotor that magnetic means (90) are provided coaxially to the wheel, which one Generate flux which penetrates the wheel, and a coil (100) is provided near the magnetic means, so that Flux changes occur due to the rotation of the wheel, which induce a current in the coil, the frequency of which is proportional to the rotational speed of the rotor. 5. Drive system according to claim 4, characterized in that a magnetic structure (58) with the stator Windings (60, 62, 64) belonging to it, and also control devices (82) to control the speed of rotation of the motor are present which are connected to the coil (100) and the windings (60, 62, 64). 6. Drive system according to claim 5, characterized in that a plurality of the magnetic devices (90) of magnet segments belong around the wheel, and the coil represents a test coil (100) in the vicinity of the magnet segments, the rotation of the wheel induces an alternating current in this coil. 7. Drive system according to claims 1, 2 or 3, characterized in that the stator has a magnetic structure (58) with windings (60, 62, 64) belonging to it, and / further - 21 409830/0725 directions (88, 90, 100) are present, which deliver a signal whose frequency depends on the speed of rotation of the engine depends, and. a control device (82) with which the signal producing Devices is connected, and depending on this signal of the windings (60, 62, 64) supplied Current is controlled to control the speed of rotation of the motor. 8. Drive system according to claim 7, characterized in that the control devices amplifier devices for a selected frequency, (114, 116, 118) with an input and ~ an output, the input being connected to the devices (88, 90, 100) supplying the signal is connected that a current control stage (140) is provided with control and load electrodes, the control electrodes with the windings (60, 62, 64) of the Motor are connected, and the control electrode is connected to the output of the amplifier, the amplifier depending on a predetermined frequency, the current control stage influences the amount given to the stator To control current, so that the motor with a speed corresponding to the given frequency • speed is operated. 9. Drive system according to claim 8, characterized in that the amplifier devices for the selected - - 22 - 40983 0/0725 Frequency one. Functional amplifier (114) with an input and an output, and that a negative feedback loop (116 _S 118) is provided, which is connected to its output and input, and a filter (116) is provided to filter out the predetermined frequency. 10. Drive system 'according to claims 1 to 9? characterized in that the motor (44) a magnetic structure · (58) having a plurality of legs (58a, 58b _S 58c) and windings (60, 62, 64) on each of these legs, in that furthermore a commutator is fixed to the stator , with sections (68, 7O ₈ , 72) individually connected to the windings via brushes (55 ₉ 56) to alternately connect the rotor to the sections of the commutator to alternately excite the windings ^ - and that a direct current source (82) is provided, which is connected via the commutator to the windings for their excitation - 11. Drive system according to claim 10 _f, characterized in that that a magnetic structure with a first (58a), second (58b) and third leg (58c) is provided, with first (60), second (62) and third (64) windings, which are connected in a star connection, and that to the commutating a first conductive ring (66) is provided coaxially with the stator and a first (68), second (70) and third (72), individually symmetrically arranged, conductive portion _f which is connected to the separate outputs of the windings, whereby the power supply (82) is connected to the common terminal of the windings and the conductive ring (66) _s resulting in a circuit 40 9830/0725 -23- from the conductive ring via the brushes (55 »56) to one of the conductive sections, around the windings successively to excite. 12. Drive system according to claims 1 to 11, for use in a cassette tape recorder, characterized in that that the drive shaft (24) forms the capstan which is used to drive the belt within the Cassette is used. 409830/0725